Materials used for a semiconductor device is extending from inorganic material to organic material. With this change, the characteristics of a semiconductor device or a fabrication process can be further optimized by using special characteristic or the like of organic materials which is not present in inorganic materials.
One such organic material may be polyimide. Polyimide has high adhesion and also has a low leak current. Thus, a polyimide film obtained by forming polyimide on a surface of a substrate may be used as an insulating layer, and it may also be used as an insulating layer in a semiconductor device.
As a method for forming such a polyimide film, a film forming method is used based on the deposition of polymerization using, for example, pyromellitic dianhydride (PMDA) and 4,4′-diaminodiphenylether including, for example, 4,4′-oxydianiline (ODA), as raw material monomers. The deposition polymerization is a method for thermally polymerizing PMDA and ODA used as raw material monomers on a surface of a substrate by sublimating them. A film forming method is also used for forming a polyimide film by evaporating the monomers of PDMA and ODA with a vaporizer, supplying the evaporated vapor of each of the PDMA and ODA to a deposition polymerization chamber, and deposition-polymerizing the same on the substrate.
In order to form a polyimide film having excellent film quality by using deposition polymerization at a low cost and within short time, it is required to continuously supply a fixed amount of a PMDA gas obtained by vaporizing PMDA and an ODA gas obtained by vaporizing ODA to the substrate. In particular, PMDA is a solid raw material and has sublimation properties. In some instances, a film forming apparatus for forming a polyimide film includes a vaporizer installed at an outer side of a film forming container in order to sublimate PMDA, a solid raw material, and supply the PMDA in the sublimated state to the film forming container.
However, the film forming apparatus for forming a polyimide film by supplying the PMDA gas and the ODA gas to the substrate has the following problems.
In order to form a polyimide film on the surface of the substrate by supplying the PMDA gas and the ODA gas, a monomer of PMDA and a monomer of ODA are required to be polymerized on the surface of the substrate. However, when the ratio between a supply amount of the PMDA gas and that of the ODA gas on the surface of the substrate is changed, a film formation rate of the polyimide film is easily changed, degrading the uniformity of film thickness, film quality and the like of the polyimide film within the surface of the substrate.
In order to make the ratio between the supply amount of the PMDA gas and that of the ODA gas uniform, it is preferred to make both the supply amount of the PMDA gas and that of the ODA gas uniform. However, when the internal pressure of the vaporizer vaporizing PMDA changes, a supply amount of the PMDA gas is changed. Also, when the internal pressure of the vaporizer vaporizing ODA is changed, a supply amount of the ODA gas is changed.
In addition, the foregoing issue is common even when a polyimide film is formed by supplying a raw material gas comprised of an aromatic acid dianhydride including the PMDA gas and a raw material gas comprised of an aromatic diamine including the ODA gas to the substrate.